Pneumatic impact device



April 19, 1960 A. R. JOHNSON ET AL 2,933,058

PNEUMATIC IMPACT DEVICE Filed June 6, 1957 2 Sheets-Sheet 1 )QLJ LrLJ 44 50 mmvroxs ARTHUR R. d0H/V50/V JOSEPH C. KEFPN A TORNEYS April 1960 A. R. JOHNSON ET AL 2,933,068

PNEUMATIC IMPACT DEVICE Filed June 6, 1957 2 Sheets-Sheet 2 Z 58 A FIG. 3

1 n RED INVENTORS ARTHUR Rz/OHNSON (JOSEPH C. KEPN ATTORNEYS PNEUMATIC IMPACT DEVICE Arthur R. Johnson, Newington, and Joseph C. Kern,

New Britain, Conn., assignors to The Branford Company, New Haven, Conn., a corporation of Connecticut Application June 6, 1957, Serial No. 664,107

20 Claims. (Cl. 121-13) This invention relates generally to pneumatic impact devices of the type used to vibrate an associated structure, and more particularly to a reciprocating piston type of impact device wherein the piston is operated by differential air pressure to give the desired impact action.

It is an object of this invention to provide a new and improved pneumatic impact device which utilizes the differential air pressure across the piston to a maximum extent in driving the piston.

It is another object of this invention to provide a new and improved pneumatic impact device which efliciently produces a high impact without the need for any rapid air exhaust and permits the utilization of miniature controls as well as an exhaust port of minimum size.

It is a further object of this invention to provide a new and improved pneumatic impact device which is readily adjustable to provide a desired amount of impact energy over a wide range and at any blow frequency desired.

It is still another object of this invention to provide a new and novel mounting arrangement for an impact device to isolate the body of the device from the vibrations of the structure vibrated in order to increase the over-all impact efficiency and protect the device from vibration fatigue.

It is a still further object of this invention to provide a new and novel pneumatic impact device which is simple in construction, inexpensive to manufacture and is of rugged and sturdy construction so as to be capable of prolonged use with no danger of breakdown.

Another object of the invention is to provide a novel and improved control arrangement for energizing the device and for regulating the speed or frequency of operation.

Other objects will be in part obvious, and in part pointed out more in detail hereinafter.

The invention accordingly consists in the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the application of which will be indicated in the appended claims.

This invention is illustrated in the accompanying drawings, wherein:

Fig. l is a vertical sectional view of a pneumatic impact device constructed in accordance with the invention;

Fig. 2 is a fragmentary enlarged view, partly in cross section, of the lower end of the device turned 90 from the position of Fig. 1 and showing the mounting arrangement;

Fig. 3 is a diagrammatic illustration of one form of control which may be utilized with the pneumatic impact device of Fig. 1, the control being in condition to cause retraction of the piston;

Fig. 4 is a fragmentary diagrammatic view showing the valves of the control of Fig. 3 in condition to cause a power stroke of the piston; and

Fig. 5 is a fragmentary diagrammatic view of a modified form of the control of Fig. 3.

nited States Patent 2,933,968 Patented Apr. 19, 1960 in accordance with the invention, a pneumatic impact device A is illustrated in Fig. 1 which comprises a casing 1 preferably cylindrical in shape formed with a plurality of laterally extending flanges 2 which, in the specific embodiment shown, are integrally formed on opposite sides of the casing 1. The flanges 2 may be mounted directly on a structure to be vibrated by means of the bolts 4. In the preferred embodiment, however, the flanges 2. are bolted to a bracket or adaptor 5 which in turn may be welded or bolted to the structure to be vibrated. The advantage in using the adaptor 5 is that it simplifies the installation of the vibrator, protects and reinforces the structure being vibrated, and provides a predetermined optimum spacing relative to the anvil 44 to be described later. Each of the bolts 4 extends through a metal sleeve 6 which is encased in a resilient bushing 8 of rubber or the like received in a suitable aperture 1t) formed in each of the flanges 2. The head of the bolt engages against a metal washer 12 which engages against a resilient annu lar pad 14 of rubber or the like on the top of the flange. A second resilient pad 15 is disposed between the flange and the associated structure or the adaptor 5 as the case may be. In this way, the casing 1 is isolated vibrationwise from the structure being vibrated. This greatly increases the efliciency of the device because it effectively reduces transfer of vibrating energy from the vibrated structure to the device A and it has the further advantage of protecting the device and its associated controls from vibration fatigue.

As shown in Fig. 1, there is a centrally arranged cylinder 18 mounted coaxially within the casing 1 and spaced therefrom to form an annular chamber 16 therebetween. The chamber 16 communicates through cylinder wall ports 19 with the interior of the cylinder 18, the upper portion of which is seated within a recess 21 within the top inner wall of casing 1. The chamber 16 has a port 22 positioned in the casing wall for receiving pressurized air as will be described more particularly hereinafter.

The casing 1 is formed with a boss 24 having a bore 26 in which is received the lower end of the cylinder 18 and a counterbore 28 communicating with a diagonal passage 30 forming the main air inlet and also the air discharge port for the device. An apertured bearing sleeve insert 32 is disposed in the bore 28 and forms a seat for the lower end of the cylinder 18. Sealing means such as an O-ring 4% is preferably employed to seal the engagement between the cylinder 18 and casing. The bottom portion of the insert 32 slidably accommodates the flanged head 43 of an impact anvil 44, and an 0- ring seal 46 is disposed between the anvil 44 and the sleeve 32. The lower end of the bore 28 is closed by a resilient annular pad 47 held in the position shown by means of a bottom plate 49 mounted by bolts 50 to the bottom of easing 1. Thus, the anvil 44 is permitted a limited axial movement within the lower portion of the sleeve 32 and by extending through the center opening of pad 47 has its lower end positioned in abutting engagement with the adaptor 5 or the structure to be vibrated as shown in Fig. 2.

Actuating means for the device of Fig. 1 is provided in the form of a freely movable piston 52. reciprocally movable in the cylinder 18. Sealing means are provided such as O-rings 54 received in grooves in the piston and engageable in sealing relationship with the inner wall of cylinder 18. The lower end of piston 52 is of reduced diameter and is adapted to strike the flanged head 43 of anvil 44 in impact producing engagement.

In accordance with the invention, means are provided to releasably hold the piston in the upper or retracted position. While many various mechanical and electrical devices could be utilized for this purpose, avery simple catch arrangement is illustrated in the drawings. Inthe specific embodiment shown, the upper end of piston 52 contains a catching recess or keeper 55 which, when the piston '52 is adjacent the upper limit of its path in cylinder 18, moves over and into retainingengagement with the piston restraining means in the form of a spring clip 57 mounted within the top of casingl. The spring clip 57 comprises a downwardly extending pair of pivotal fingers 59 pivoted on pin 56 in a threaded bushing '58. The fingers 59 are biased apart to engage within the piston recess 55 by means of a spring 6% the compression of which may be adjusted by an adjusting screw '61 which is held in adjusted position by the lock nut .62. It can be seen that the inward movement of the adjusting screw 61 compresses the spring 6t) and by thus increasing the force biasing the fingers apart, increases the piston restraining force.

In the operation of the pneumatic device of Fig. l, the device is first conditioned by applying air under pressureto the chamber 16 through the casing port 22. For maximum impact force, the pressure in chamber 16 is preferably selected so that it is close to line pressure when the piston 52 is positioned at the upper end of cylinder 18. The piston 52 may be conveniently raised to latched position by air pressure applied through port 30. To facilitate setting up the device, an indicator B is provided to show when the piston is in its uppermost position. Many forms of indicators could be used and there is shown in the'drawings by way of illustration a microswi'tch 63 for connection to a visual or audible signaling means (not shown) which microswitch is actuated by a spring pressed plunger 54 extending through an orifice 65 into position for engagement by the top of the piston whenthe piston is fully elevated.

By adjusting the air pressure in chamber 16 to nearly line pressure, the upward movement of the'piston atits upper limit of travel is effectively cushioned and a maximum return striking or vibrating force is assured. When pressurized air is applied to the underside of the piston 52 to raise the piston thereafter, only sufficient differential pressure is-required to move the piston upwardly until the spring clip fingers 59 engage within the piston catching recess 55 and thus hold the piston in its upper position. By proper design of the camming surfaces of the fingers 59 and recess 55, the engaging force in the spring clip may be made very slight compared with the force required to disengage the piston.

To produce the working or impact stroke of the piston 52, the port 30 is vented to reduce the pressure on the lower side of piston 52 to substantially atmospheric in order to create a maximum pressure differential across the piston and the adjusting screw 61 is preferably set so that the spring clip will not release the piston until the pressure on the piston lower side is substantially atmospheric and maximum pressure differential is attained. A particular advantage in so adjusting the clip 57 is that the speed with which venting takes place through the port 30 is not critical. After the pressure on the lower end of the piston has been vented, the air pressure in chamber 16 and cylinder 18 above the piston becomes sufficient to disengage the piston 52 and driveit downwardly into vibration producing contact with the impact anvil- 44. Maximum efliciency is attained by adjusting the holding force of the spring clip so as not to release the piston until a maximum pressurev differential exists across the piston. After the piston has struck anvil 44 air pressure is admitted once again to the lower side of piston 52 to move it upwardly and repeating the same action described above."

As described above, maximum impact force is attained by adjusting the pressure inbchambei' 16 to a pressure close to and only slightly less than available line pressure. However, if less impact force is desired, it is an advantage of--the invention that the device will operate with equal efiiciency with lower pressures in chamber 16. This is accomplished by adjusting the retaining force of the holding means 57 so that release of the piston occurs at maximum pressure differential as just described. Normally, it will not be usual or necessary to separately adjust the spring clip or other holding means after the device has been mounted in a particular installation since the pressure .in chamber 16 can be maintained substantially constant at the value desired for that particular installation. However, it is within the purview of the invention to include'autornatic adjusting means for the spring clip 57 or other holding means which are responsive to any variation'of the back pressure on the piston if this is found to be desirable.

It will thus be seen. that there has been provided a novel and improved pressure actuating impact device which has its most outstanding feature in that a full use is made of line pressure to drive thepistoninto' impacts producing engagement with an i-anvil. It is :.not necessary, as in previous designs, to provide anarrangement for quickly exhausting pressure on one side of the piston; and, therefore, not only may simplified controls for the device be employed, but in addition the parts of the device itself are extremely simple and'few.

While various arrangements may be used-to alternately apply pressurized air to the bottom of the piston through port 30 and release the same, thereis shown in'Figs. 3 and4 one form of simple control which may be utilized effectively for optimum results. ;As will be apparent from the following description, the control is exceedingly simple and compact and maybe-mounted, if desired, in a-manifold attachedto the casing 1. Airatrline pressure from a suitable source (not shown) is applied to three-way valve at the inlet 71 and by conduit 72 to the three-way'valve 73 and by conduit 74 through check valve 75 and pressure reducing valve 76 to'the inlet 22 of easing 1. -As will be-apparent, by.suitable adjustment of pressure reducing valve 76a predetermined minimum pressure may be maintained constantly in the chamber 16 to insurethat the desired impact pressure will be applied to the piston 52.

In the normalposition of three-way valve 73shown in Fig. 3,.the pressurized air from inlet 71 is admitted to conduit 77 which connects with the left hand end of valve 70 thus moving the piston 7 0a thereof 'to the right hand position shown which closes the exhaust port70b and .permits thepressurizedainfrom inlet 7;1-.to pass directly to conduit 78 w-hich in .turn is-conneeted-to the inlet port 30 of casing .1. Thus in the condition of the control shown in Fig. 3, which occurs as a result of applying line pressure to inlet 71,-air'pressureis applied to the pneumatic impact device through'valve 7 0 to raise or-retract the piston 52.

-A bleed line'80 containing a check valve 81, a; throttle valve-82, and'exhaust valve 83 connects the conduit 78 to the left hand side-of three-way valve 73. Thus after a suitable time-interval determined primarily by the setting of valve 82, sufficient pressure will build up on the-piston 73a of valve 73 to move the piston to the righthand position-shown in Fig. 4 which closes theinlet to-conduit 72 and exhausts conduit'77. Upon this happening, the piston 7.0a moves .to. the left hand POSitiOIlwShOV/D in Fig. 4

which-closes the pressurized air inlet and vents the conduit 78. Thusthepressurized airin frontofpiston 52 of the pneumatic impact device is permitted to escape and when this is substantially;complete, the back pressure on piston 52 will disengage the piston 52 from the restraining means 57 causing a rapid impact stroke to take place.

-The .air pressure which has been applied to the threeway valve 73 to cause the impact s'tpoke to take place is subsequently dissipated through the exhaust valvef83 which permitsthe valve 73 to return to the position shown in Fig. 3 which causes valvelt) to-again move to the right to admit air to the cylinder and repeat the cycle. As will be readily apparent, the speed of operation of the pneumatic impact device can be readily selected by adjustment of the valves 82, 83. Care should be taken, however, to insure that sufficient time elapses on the up-stroke of piston 52 to insure that it will be engaged by the latch 57 for only in this way will the maximum impact and efficiency of the device be attained. By use of the indicator B, the operator can readily check whether the device is operating in the desired manner.

In the modified portion of the control shown in Fig. of the drawings, an air governor comprising an adjustable pressure responsive ball valve 90 is disposed between the valve 81 and the conduit 78. By adjusting the spring 91, the ball valve can be set to release only after substantially full pressure has been applied to the piston 52 which is realized only when the piston' 52 has attained its uppermost position and is latched by the retaining means 57. As in the first modification, the speed or frequency of operation can be attained by adjustment of the valves 82, 83 but with the assurance that regardless of the setting the device will not fire, i.e., deliver an impact stroke until after the piston 52 has been fully raised.

It thus will be seen that with a simple control of compact and eflicient design it is possible to operate the pneumatic device of the present invention in an auto matic and efficient manner. The device may be adjusted for operation over a wide range of frequencies and also for operation over a wide range of impact energy, thus rendering the device suitable for use throughout a wide variety of installations.

Inasmuch as the embodiments of the invention will be subject to variation and modification within the skill of the art, all such variations and modifications are intended to be included within the scope of the invention.

We claim:

1. A pneumatic impact device comprising a cylinder and a piston slidably mounted therein, means to apply air pressure simultaneously to opposite sides of the piston at a difierential such that the piston is moved toward one end of the cylinder, retaining means for yieldingly holding the piston at said one end of the cylinder, and means for releasing air from the other end of the cylinder, said retaining means being adjustable to release the piston responsive to the release of substantially all the air pressure from said other end of the cylinder.

2. A pneumatic impact device comprising a cylinder and a piston slidably mounted therein, means for applying air pressure to one side of the piston, means to simultaneously apply air at a higher pressure to the other side of the piston to move the piston toward one end of the cylinder, means for releasing air from said other side of the piston, and means for retaining the piston at said one end of the cylinder, said means being releasable by a predetermined diiferential pressure applied to the cylinder.

3. A pneumatic impact device comprising a cylinder, a freely movable piston in said cylinder for reciprocation therein by differential air pressure on opposite sides thereof, a first air port adjacent one end of said cylinder on one side of said piston, a reservoir of air under pressure in constant communication with said air port, a second air port adjacent the other end of'the cylinder, means alternately to connect said second air port to an associated source of air under higher pressure, for moving said piston towards said one end and to discharge air from said cylinder, piston restraining means at said one end of said cylinder for releasably engaging said piston in holding relationship when said piston is moved toward said one end, said piston restraining means being adjustable to provide a selected piston holding force to permit release of the piston when said differential air pressure is at a preselected level.

4AA pneumatic impact device comprising a cylinder,

a freely movable piston in said cylinder for reciprocation therein by difierential air pressure on opposite sides thereof, an air port adjacent each end of said cylinder on opposite sides of said piston, said ports arranged to be connected to an associated source of air pressure, a catching recess in one face of said piston, a piston restraining spring clip at the end of said cylinder corresponding to said recessed piston face, said clip being insertable into and yieldingly engageable with said piston recess when said piston travels to said cylinder end, said spring clip being arranged to release said piston when said differential air pressure is at a level sufiicient to overcome the clip engaging force, a reservoir of air under pressure in constant communication with the air port adjacent the spring clip cylinder end, and means alternately to connect the other air port to an associated source of air under higher pressure and to discharge air from said air cylinder.

5. A pneumatic impact device comprising a cylinder, a casing positioned around said cylinder in spaced apart relation to form an air reservoir, a supply of air under pressure in said reservoir, an opening in one end of said cylinder communicating with said reservoir, a freely movable piston in said cylinder for reciprocation therein by diiferential air pressure on opposite sides thereof, means for alternately applying air under pressure from an outside source to the opposite end of said cylinder and releasing the air therefrom, a catching recess in the end of said piston facing said one end of the cylinder, and an adjustably tensioned spring clip at said one end of said cylinder arranged to enter into and releasably engage said piston catching recess when said piston is moved toward said cylinder one end, said spring clip being arranged to release said piston to permit movement towards the opposite end of said cylinder when said differential air pressure is at a level sufiicient to overcome said clip catching force.

6. A pneumatic impact device comprising a cylinder, a casing positioned around said cylinder in spaced apart relation to form an air reservoir, a supply of air under pressure in said reservoir, an opening in one end of said cylinder communicating with said reservoir, a freely movable piston in said cylinder for reciprocation therein by differential air pressure on opposite sides thereof, means for alternately applying air under pressure to the opposite end of said cylinder and releasing the air therefrom, an impact anvil movably mounted on said casing at said opposite end of the cylinder engageaole by, said piston, a catching recess in the end of said piston facing said one end of the cylinder, and an adjustably tensioned spring clip at said one end of the cylinder arranged to releasably engage in said piston catching re cess when said piston is moved toward said cylinder one end, said spring clip being arranged to release said piston to permit impact with said anvil when the diiferential air pressure is at a preselected level.

7. A pneumatic impact device comprising a housing having means for attachment to an associated structure, an anvil supported by the housing for engagement with the associated structure and movable relative to the housing, a cylinder supported by the housing in alignment with the anvil, a piston in the cylinder, means for maintain,- ing a preselected air pressure in the cylinder on the side of the piston opposite from the anvil, means for alternately admitting air under higher pressure between the piston and anvil and releasing the air therefrom, and retaining means for yieldingly holding the piston away from the anvil.

8. A pneumatic impact device comprising a housing having means for attachment to an associated structure, an anvil supported by the housing for engagement with the associated structure and movable relative to the housing, a cylinder supported by the housing in alignment with the anvil, a piston in the cylinder, means for maintaining a preselected air pressure in the cylinder on the side of the piston opposite from the anvil, means for '7 alternately admitting air under higher pressure between the piston and anviland releasing the-air therefrom, and a catch for yieldingly engaging and-holding the-piston at the end of'the'cylinder away from the anvil, said catch being disengagea-ble by the application of suflicient force to the piston.

9.. A pneumatic impact device comprising a housing having meansfor attachment toan associated structure, an anvil supported-by the housing for engagement with the associated structure and movable-relative to the housing, a cylinder supported by the housing in alignment with the anvil and communicating at its end opposite from the anvil with the interior of the housing, said interior of the housing forming a reservoir for air under pressure, means*formaintaining a minimum air pressure invsaid rcservoirga-piston in'the cylinder, means for alternately admitting air under pressure between the piston and anvil and releasing the air therefrom, and means at the end of the cylinderopposite-from the anvil for holding the piston until a :minimum predetermined force is applied to the piston in the direction of the anvil.

10. A pneumatic impact device comprising a housing having means for attachment to aniassociated structure, an anvil supported by the housing for engagement with the associated structure and movable relative to the housing, a cylinder supported byithe housing in alignment with the anvil and communicating at its end opposite from the anvil with the interior of the housing, said interior of the housing forming a reservoir for air under pressure, means for maintaining a minimum air pressure'in'saidreservoir, apiston in the cylinder, means for alternately admittingair under ,pressure between the piston and anvil and releasing the :air therefrom, and

' a catch located at theend of the cylinder oppositefrom' the anvil and engageaole bythe piston, said catch having an adjustable holding force whereby it may be set to release the piston upon the application of a selected force to the pistonin the-direction of theanvil.

11. A pneumatic impact device comprising a cylinder and a piston slidably mounted therein, means to apply a differential air pressure to opposite sides of the piston to reciprocate the sameiincluding means for maintaining'a pre-selected air pressure at one end of the cylinder and means for alternately supplying air at a higherpressure and exhausting said air at the other end of the cylinder, retaining means for releasably holding the piss 7 ton at said one end of :the cyiinder,and 'signalinglmeans including a switch member engageable by the piston when the piston is at said one end of the cylinder ifor indicatingwhen the piston is engaged by the retaining means. i

12. In a pneumatic impact device, a casing, an anvil movably mounted on the casing, a piston in the casing adapted to engage the anvil, bolt means to secure the casing on an associated structure with the anvil in engagement therewith, and resilient means separating the casing from the bolt means and the associated structure.

13. A pneumatic impact device comprising a vcasing, a cylinder positioned within said casing, a piston in said cylinder for reciprocation therein by differential air .pressure on opposite sides thereof, an impact anvil movably mounted on the casing at one end of the cylinder and engageable in vibration producing (contact by. said piston,

'means for mounting said casing on an associated structure with said anvil only in vibration producing contact with said structure, and resilient means separating :said casing from sald mounting means and associated struc- 1 ture.

14. A pneumatic impact device comprising a casing,

"a cylinder positioned within-said casing, a piston in said cylinder'for reciprocation therein :by differential air pressure on opposite sides thereof, an impact anvil movably mounted on the casing at one end of'the cylinder for engagement by said "piston, a laterally extending flange ori the casing on opposite sides ofsaid anvil, a plurality of mounting bolts extending through said flange and securing .said casingto an {associated structure with said anvilronly'in vibrationrprodueing contact with saidstructure, and .a resilient vspacer separating said flange from said mounting bolt and t associated structure.

15. A pneumatic impact device comprising a casing, anvanvil movably mounted atone end of the casing, a cylindersupported by-the casingin alignment with the anvi1,-.-a:5fr ee,p'istonslidably mounted in the cylinderr for engaging the-anvil, :meansto apply a differential .air pressure to. opposite :sides of therpiston .to reciprocate the same, an attaching bracketadaPted to be mounted on a structure'to the-vibrated having a. surface engaged by the anvil, and means for mounting the casing on the bracket including a resilient spacer ,therebetween.

116. Apneumatic impact device Comprising atcylinder containing a slidable piston, an anvil movably. mounted at one end of the cylindertor impact by the piston, means .for.maintaining aiselected .air pressure on 1 the opposite end of -the cylinder, means for applying a'rhigher air pressure between the anvil and piston to move the piston 'totsaidopposite end of the cylinder, a releasable catch at said opposite end of the cylinder engageable by the cylinder, means for releasing the air from vbetween the anvil andpiston, and means responsive to the air pressure betweentheanvil andrpiston for delaying (open ration of .the last named ,means .until the piston has been engaged by thecatch.

17. A pneumatic impactdeyice comprising a cylinder and a pistoneslidably {mounted therein, an anvilmovably mounted at one end of the cylinder ,forimpact by the piston, means-for maintaininga selected air pressure on the opposite end of the cylinder,-restraining -means at said opposite end of the cylinder for holding thet-piston in retracted position until a minimum force is applied thereto in the direction of the anvil, and means for alternately applying a higher air, pressure between the anvil and' pistonand. releasing the air therefrom comprisingra three-wayrvalve connected to said one end of the .eylinder having a first position for admittingair from an associated source of air under-pressure and a second 'position for venting the cylinder, means for moving the valve to said second position, and delay means for preventing operation :of the last-named means until the pistonis in engagementwith the restraining means.

18. A pneumatic impact device comprising. a cylinder and a piston slidably mounted ,in-the cylinder, an anvil movably upported at .oneend oi thecylinder for impact by the piston, and means for alternately applying air pressure between the anvil and piston and releasing the air therefrom comprising a cylinder port adjacent the anvil, a three-Way'valve lconnectedon one side to the port and connectibleat its other side to a source ofsair under pressure, said-three-way valve having a first position venting the port to atmosphere and a second position admitting air under pressure from the source to the port, pressure responsive .means for moving the, valve from first position to second position, a second threeway valve connected at oneside to said pressure responsive means and; conuectible at its other side to thesource of air .under pressure, saiddast-named valve havin -.8

first .positionior"admitting airsunder pressure =to said pressureresponsive means and asecond-position for vent ingqs'aid pressureresPQnsive means :to atmosphere-second pressure re ponsive neans'itor moving the second valve to its second position, and means for applyingair under pressure to .theisecond pressure responsive means {comprising a restricted connection communicating at one end with said port.

actuated valve piston which is biased to a first position in which the port is exhausted to atmosphere and movable by air pressure to a second position in which air under pressure from an associated sourceis admitted to the port, a second three-way valve communicating with the pressure-actuated piston of the first three-way valve and having a pressure actuated valve piston biased to a first position at which air from said outside source is applied to the pressure-actuated piston of the first threeway valve and movable by air pressure to a second position in which the air applied to the pressure-actuated piston of the first three-way valve is vented, and a restricted passageway extending from between the first threeway valve and port to the pressure-actuated piston of the second three-way valve.

20. A pneumatic impact device comprising a cylinder and a piston slidably mounted therein, an air reservoir communicating with one end of the cylinder, means forming a port communicating with the other end of the cylinder, and means for applying a differential air pressure to opposite sides of the cylinder and piston utilizing a source of air under pressure comprising a first conduit connected to the air reservoir containing a one-way valve and a pressure reducing valve, a first three-way valve connected to said port having a pressure-actuated valve piston which is biased to a first position in which the port is exhausted to atmosphere and movable by air pressure to a second position at which air under pressure from said source is admitted to the port, a second three-Way valve communicating with the pressure-actuated piston of the first threeway valve and having a pressure actuated valve piston biased to a first position at which air under pressure from said source is applied to the pressure-actuated piston of the firstthree-way valve and movable by air pressure to a second position in which the air applied to the pressure-actuated piston of the first three-way valve is vented to atmosphere, and means for applying air under pressure to the pressure actuated piston of the second threeway valve comprising conduit means extending from between the first three-way valve and said port to the pressure-actuated piston of the second three-way valve, said conduit means including a valve for delaying actuation of the second three-way valve.

References Cited in the file of this patent UNITED STATES PATENTS 2,241,184 Clark May 6, 1941 2,290,256 Souter July 21, 1942 2,583,645 Hannen Jan. 29, 1952 2,786,450 Iacobus et a1 Mar. 26, 1957 2,821,170 Jacobus June 28, 1958 FOREIGN PATENTS 821,437 Germany Nov. 19, 1951 

